In the design of a civil jet transport, such as the Boeing 777 shown in Fig. 6.27, the choice of engine size is usually based on having a 300 feet per minute rate-of-climb capability at the top of climb to cruising altitude. This is a safety margin. Assume the following cruise conditions at top of climb for the Boeing 777_LID= 18, altitude = 31,000 , M_ = 0.0 85, W = 550,000 lb. (a) Obtain an equation for the required engine thrust, assuming that the climb angle is so small that L = W. (b) Calculate the required engine size (in terms of sea-level static thrust), and compare your result with the designers’ engine choice for the Boeing 777, which is two engines of the Rolls-Royce T!!· type with a sea-level static thrust of34,000 each. However, using the top-of-climb criteria discussed here, the resulting engine thrust is usually quite ample for take-off.
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